Determination of the Triad Sequence Distribution and the cis/trans Linkage Configurations at the Cyclic Anhydride Units in the Alternating Copolymers of Maleic Anhydride and Citraconic Anhydride with Styrene and other Donor Monomers

Abstract

Copolymers of maleic anhydride (MA or 0) with styrene (ST or 1) and copolymers of citraconic anhydride (CA or 0) with ST(1) were prepared with a radical initiator at 50°C in CC1₄ (the dielectric constant ε =2.24) and in highly polar N,N-dimethylformamide (DMF, ε=36.7). ¹³C NMR spectroscopy was used to determine the ST(1) centred triad mole fractions (Fₒ₁ₒ, Fₒ₁₁+₁₁ₒ)and F₁₁₁) and the mole fraction of the cis/trans linkage configuration at the cyclic anhydride units (Fcis and Ftrans). Non-linear least squares (NLLS) minimisation techniques was applied for the examination of the applicability of various copolymerisation models; the terminal model, the penultimate unit effect model, the complex participation model, the complex dissociation model and the so-called "comppen" model. The triad distribution data and the overall copolymer composition were used for the NLLS examination of the copolymerisation models, in combination with the test functions a and b. For both MA-ST copolymers and CA-ST copolymers, the copolymerisation models which incorporated a participation of the complex were most consistent with the data; for the MA-ST copolymers, the complex participation model, while for the CA-ST copolymers the comppen model showed the best fit.